Humidity measuring probe



Nov. 15, 1955 c. E. oHLHElsl-:R 2,723,557

HUMIDITY MEASURING PROBE Filed April 6, 1951 "j lIhr/@www ATTORNEYINVENTOR HUMIDITY MEASURING PROBE Carlton E. Ohlheiser, Silver Spring,American Instrument Company,

Md., assigner to Inc., Silver Spring,

This invention relates to humidity measuring devices, and moreparticularly to an improved probe device for detecting and measuringmoisture in comminuted solid materials or seed material, such as grainor the like.

A main object of the invention is to provide a novel and improvedhumidity measuring probe which is simple in construction, which involvesonly a few parts, which is easy to manipulate, and which provides aconvenient and accurate means of determining the moisture content ofmaterials such as grain,l seeds, comminuted inorganic material such assand, or other accumulated material of porous character, such as cotton,vegetable iibres, or the like.

A further object of the invention is to provide an improved moistureprobe whichI is inexpensive to manufacture, which involves no movingparts, and which provides true and accurate indications of the moisturecontent of the material being tested.

A still further object of the invention is to provide an improvedmoisture testing probe for measuring the moisture content of grain orsolid comminuted materials, said probe being compact in size, light inweight and being suitable for use with portable electrical hygrometryapparatus.

A still further object of the invention is to provide an improvedhumidity-measuring probe of the electrical type which may be readilyemployed to measure the moisture content of grain and similar materials,said probe including conveniently operated means for sampling the air inthe material being tested and for accurately measuring the moisture inthe air, provision being made for sampling the air at a considerabledepth in the material and for preventing possible errors due to thedifferent moisture content of the outside air, the sampled air beingdrawn over the surface of the electrically-responsive sensing element ofthe probe in a substantially uniformly distributed manner, whereby rapidand accurate indications may be obtained.

Further objects and advantages of the invention will become apparentfrom the following description and claims, and from the accompanyingdrawings, wherein:

Figure 1 is a fragmentary side elevational view, partly in longitudinalcross-section, of an improved humidity measuring probe constructed inaccordance with the present invention.

Figure 2 is a cross-sectional view taken on line 2 2 of Figure 1.

Referring to the drawings, the humidity measuring probe is designatedgenerally at 11 and comprises an elongated, rigid sleeve member 12 whichhas rigidly secured in its lower end portion, as viewed in Figure 1, theannular ring member 13. Designated at 14 is a downwardly-facing sockethaving a peripheral flange 15 which is clamped against ring member 13 byan annular ring nut 16 threadedly engaged inside sleeve member 12.Mounted in socket 14 is a three-prong humidity sensing unit 17 of theelectrical type, similar to the TH-l Humidity Sensing Elementmanufactured by the American In 2,723,557 Patented Nov. 15, 1955strument Company, Inc., of Silver Spring, Maryland, and described in mycopending patent application Serial No. 738,441, led March 3l, 1947, forHumidity Measuring Apparatus. The humidity sensing unit 17 comprises aninner tubular form 18 carrying bilar-Wound conductors covered by a thinlayer of hygroscopic material whose electrical conductivity varies inaccordance with the moisture content of the air to which it is exposed.Mounted axially inside said form 18 is a temperaturesensitive resistor19. An apertured plastic outer shell 20 is provided on the unit 17, asshown. As fully described in the above mentioned copending application,the elements of the unit 17 are connected to three prongs 21 which arereceived in the socket 14. Connected to the terminals of the socket arethe insulated conductors 22 which extend upwardly through the sleeve 12and are connected to the prongs 23 of a conventional male connector unit24 secured to the top end of the sleeve 12. Designated at 25 is athree-wire ilexible cable provided at one end with the conventionalfemale plug 26, engaging and secured to the male plug 24, and providedat its other end with the conventional plug 27 adapted to be connectedto the electrical indicator, for example, to a Type MB-l BatteryOperated Portable Indicator, manufactured by the American InstrumentCompany, Inc., of Silver Spring, Maryland.

Threadedly secured in the lower end of the sleeve 12 is a anged ring 28,and rigidly secured on said ring is the hollow probe tip 29.v Tip 29 isformed of porous metal, such as sintered metal particles, and comprisesa cylindrical body portion 30 which surrounds the major portion of thesensing unit 17, and a tapered conical end portion 31, which is taperedsubstantially to a point to facilitate the insertion of the probe to aconsiderable depth into a quantity of grain or other material whosemoisture content is to be measured.

Secured to the sleeve 12 near its top end is an upwardly and outwardlyprojecting conduit fitting 32 to which is Secured the rubber bulb 33.Designated at 34 is a conduit, such as copper tubing or the like, havingone end secured in tting 32 and extending through the sleeve 12. Theother end of conduit 34 extends through and is centrally secured in thesocket 14, establishing communication between the rubber bulb 33 and thechamber 35 defined within the spongy metal cylindrical body 30 of tip29, which contains the humidity-sensing element 17. f

In operation, the probe is inserted into the grain, or other materialwhose moisture content is to be measured, to a considerable depth. Therubber bulb 33 is alternately squeezed and released a number of times toexpel the air originally in the chamber 35 and to draw in air from thematerial surrounding the probe tip 29. The bulb 33 is alternatelysqueezed and released a suiiicient number of times to completely ushchamber 35 with the moisture-laden air around the grain or othermaterial being tested. The porosity of the wall 30 allows a freebreathing action, whereby the moisture-laden air completely permeateschamber 35, and whereby the entire surface of the humidity sensingelement is uniformly exposed to said moisture-I aden air. Said air alsopasses freely through the cylindrical form 18 around thetemperature-sensitive resistor 19, whereby the temperature of the air ismeasured simultaneously with its moisture content, and whereby therelative humidity of said air may be rapidly determined by theassociated indicator, in the manner described in the above-mentionedcopending patent application.

It will be noted that the chamber 35 is sealed olf from the space in theupper portion of sleeve 12, whereby the air in said upper portion cannotaffect the readings obtained by the use of the probe.

Any suitable pump device may be employed in place of the rubber bulb 33.For example, a mechanically operated pump device may be connected to thetting 32, such as the Brewer Automatic Pipetting Machine, model 120,manufactured by Baltimore Biological Laboratories, Baltimore, Maryland.This pump device is arranged so that it may be adjusted tol provideeither continuous suction, or alternate suction and exhaust, similar tothat produced by the alternate squeezing and releasing of the bulb 33.The use of a mechanical pump device as above described is particularlydesirable where the moisture content of the material is tested over along period of time, or where the probe is employed in conjunction witha recording device or with an automatic humidity control apparatus.

It will be further noted that by providing a breathing action at theporous metal tip 29, said tip is rendered self-cleaning, since smallparticles of material drawn into the pores of the tip during the suctionportion of the breathing cycle will be expelled during the exhaustportion of said breathing cycle.

While a specific embodiment of an improved humidity measuring probedevice has been disclosed in the foregoing description, it will beunderstood that various modiiications within the spirit of the inventionmay occur to those skilled in the art. Therefore it is intended that nolimitations be placed on the invention except as defined by the scope ofthe appended claims.

What is claimed is:

l. A humidity-measuring probe comprising an elongated rigid tubular bodymember, a relatively small hollow tip secured on the end of said bodymember, a female socket sealingly secured in the end of said tubularbody member facing said hollow tip and arranged to seal said tiprelative to said body member, a pronged electrical humidity-sensingclement mounted in said socket and housed in said hollow tip, said tipbeing made of spongy metal, a closed flexible bulb secured to said bodymember, a conduit extending through said body member and socket andconnecting the interior of said bulb to the interior of said hollow tip,whereby a breathing action is provided at said tip when said bulb isalternately squeezed and released, to dislodge particles of cloggingmaterial from said tip, and a plurality of electrical conductorsconnected to the terminals of said socket and extending through saidtubular body member.

2. A humidity-measuring probe comprising an elongated rigid tubular bodymember, a relatively small hollow tip secured on one end of said bodymember, a female socket sealingly secured in said one end of the bodymember facing said hollow tip and arranged to seal said tip relative tosaid body member, a pronged electrical humidity-sensing element mountedin said socket and housed in said hollow tip, said tip being made ofspongy metal, a closed flexible bulb secured to said body memberadjacent the other end of said body member, a conduit extending throughsaid body member and said socket and connecting the interior of saidbulb to the interior of said hollow tip, whereby a breathing action isprovided at said tip when said bulb is alternately squeezed and releasedto dislodge particles of clogging material from said tip, and aplurality of electrical conductors connected to the terminals of saidsocket and extending through said tubular body member.

3. A humidity-measuring probe comprising an elongated rigid tubular bodymember, a relatively small hollow tip secured on one end of said bodymember, a female socket sealingly secured in said one end of said bodymember facing said hollow tip and arranged to seal said tip relative tothe body member, a pronged electrical humidity-sensing element mountedin said socket and housed in said hollow tip, said tip being made ofspongy metal, a closed flexible bulb secured to said body memberadjacent the other end of said body member, a conduit extending throughsaid body member and socket and connecting the interior of said bulb tothe interior of said hollow tip, whereby a breathing action is providedat said tip when said bulb is alternately squeezed and released, todislodge particles of clogging material from said tip, an electricalconnector secured in said other end of the body member, and a pluralityof electrical conductors extending through said body member andconnecting the terminals of said socket to the terminals of saidelectrical connector.

4. A humidity measuring probe comprising an elongated rigid body member,a relatively small hollow tip secured on the end of said body member,said tip being made of porous rigid material, a humidity-sensing elementin said tip, means sealing said tip with respect to the body member, aclosed ilexible bulb connected to said body member, and a conduitconnecting the interior of said bulb to said hollow tip, whereby abreathing action is provided at said tip when said bulb is alternatelysqueezed and released, to dislodge particles of clogging material fromsaid tip.

References Cited in the le of this patent UNITED STATES PATENTS2,105,683 Burdick Jan. 18, 1938 2,151,404 Gaus et al Mar. 21, 19392,381,299 McCulloch Aug. 7, 1945 2,435,632 Mabey Feb. l0, 1948 2,494,628Oberding Jan. 17, 1950 2,526,636 Colman Oct. 24, 1950

